1. Field of the Invention
The present invention relates to a disk driving apparatus and a disk driving method. More particularly, the present invention relates to a disk apparatus and a disk driving method, which are capable of causing disk-shaped recording media, such as audio CDs (Compact Disks) CD-ROMs (Read Only Memories), video CDs, and DVDs (Digital Versatile Disks), to be efficiently driven rotationally.
2. Description of the Related Art
As methods for rotationally rotating disk-shaped recording media (hereinafter appropriately referred to simply as "disks"), such as CD-ROMs when they are reproduced, a constant angular velocity (CAV) method and a constant linear velocity (CLV) method are known. In the CAV or CLV method, a disk is rotationally driven at a fixed rotational velocity (number of rotations) or linear velocity, respectively, from its innermost region to its outermost region.
Meanwhile, in disk drives for reproducing, for example, a CD-ROM, a disk is rotationally driven by the CLV method so as to read data always at a fixed data rate. Therefore, the rotational velocity of the disk becomes faster the further inward the region being reproduced (accessed) is located, and in a CD-ROM or the like, the rotational velocity in its innermost region becomes approximately 2.5 times as high as that in the outermost region.
That is, when, for example, an 8.times. speed reproduction of a CD-ROM is performed, its rotational velocity is approximately 4,000 rpm (revolutions per minute) in the innermost region in comparison with 1,600 rpm in the outermost region.
At present, there has been realized an 8.times. speed reproduction disk drive having a mechanical system capable of stably rotating a CD-ROM at approximately 4,000 rpm or less. However, as described above, a CD-ROM is rotationally rotated at approximately 4000 rpm or less only in the innermost region thereof, and its rotational velocity decreases the further toward the outermost region the reproduction position is located.
Therefore, in this case, the maximum performance of the mechanical system can be exhibited only when the innermost region is reproduced, and in the outermost region, the performance is not effectively utilized.
Accordingly, there is a method of rotationally rotating the outermost region at approximately 4,000 rpm. In this method, the rotational velocity in the innermost region becomes approximately 10,000 rpm, which exceeds the limit of the mechanical system. Further, if the disk is rotated at a rotational velocity exceeding the limit of the mechanical system, vibrations of the disk drive, resulting from decentering or an eccentric center of gravity of the disk, become strong, and it becomes difficult to stably read data. Therefore, there occurs a need to strengthen the mechanical system, resulting in a high-cost of the apparatus and a complex design.
Further, since, as described above, the CD-ROM is reproduced by a CLV method in which the linear velocity is fixed, i.e., the rotational velocity differs according to the reproduction position (radius), problems arise in that when data is read by performing a long-distance traverse from the innermost region to the outermost region, it takes time.
More specifically, when a traverse is performed, it is necessary to change the rotational velocity of the CD-ROM from a value appropriate for a position before a traverse to a value appropriate for a position after the traverse (for example, when a traverse from the innermost region to the outermost region is performed, it is necessary to decrease the rotational velocity from approximately 4,000 rpm to approximately 1,600 rpm). Therefore, after the traverse, the reading of data cannot be started until the time required for the traverse has elapsed. This fact is a factor for causing the seek time to deteriorate.
Accordingly, there is a method in which a mechanical system for rotationally rotating a CD-ROM having a large torque capable of performing rapid acceleration and deceleration is used. When such a mechanical system is used, the apparatus becomes enlarged and the cost thereof is increased, and when rapid acceleration and deceleration is performed, consumption of power increases.